1. Field of the Invention
The present invention relates to a measuring method of flying height of a thin-film magnetic head, which is flying above a rotating magnetic disk, and a magnetic recording and reproducing method using the measuring method of flying height in a magnetic disk drive apparatus. Further, the present invention relates to a magnetic disk drive apparatus for carrying out the measuring method of flying height and the magnetic recording and reproducing method.
2. Description of the Related Art
The thin-film magnetic head included by a magnetic disk drive apparatus hydrodynamically flies with a predetermined gap (flying height) above a magnetic disk, which is a rotating magnetic recording medium, when writing and reading a signal. In this flying state, the thin-film magnetic head writes data signals by applying a signal magnetic field to the magnetic disk by using an electromagnetic coil element, and reads data signals by receiving a signal magnetic field from the magnetic disk by using a magnetoresistive (MR) effect element.
In correspondence with increase in recording density accompanying increase in capacity and reduction in size of magnetic disk drive apparatuses in recent years, the track width of thin-film magnetic heads is set at a smaller value. In order to avoid reduction in writing and reading ability apprehended due to this reduction in the track width, the flying height is reduced more in recent magnetic disk drive apparatuses, and the flying height is actually set at about 10 nm or less.
The flying height having such an extremely small value needs to be controlled stably for avoiding a thermal asperity and crash and for keeping favorable write and read characteristics. As a control method of the flying height, for example, U.S. Pat. No. 5,991,113 discloses the art for adjusting flying height by providing a heating element in a thin-film magnetic head, and by causing a head element end to protrude toward a magnetic disk by the heat generated from the heating element.
As the flying height has such an extremely small value, the influence of the ambient temperature and atmospheric pressure inside the magnetic disk drive apparatus becomes considerably large. Thus, as a countermeasure against the change in flying height due to ambient temperature, the ambient temperature is measured by providing a temperature sensor in the magnetic disk drive apparatus, and based on the measurement value of the temperature, the control of supplying the electric power to the above described heating element for flying height adjustment is performed, for example.
Meanwhile, the atmospheric pressure in the magnetic disk drive apparatus changes in accordance with the use of the apparatus, for example, in a highland and or in an airplane. As the countermeasures against the change in flying height by the atmospheric pressure, for example, Japanese Patent Publications Nos. 10-177774A and 6-150522A disclose the arts in which the flying height is controlled by changing the rotational frequencies of the magnetic disks based on signals from atmospheric sensors. In the art disclosed in Japanese Patent Publication No. 6-176557A, a magnetic disk drive apparatus, provided with a heater, a cooling fan and fin, and a pressure sensor, is sealed in a sealed glass container, whereby the pressure change inside the container is adjusted by controlling temperature, and thus, the flying height change due to a pressure change is suppressed. Further, Japanese Patent Publication No. 10-222945A discloses the art of checking a flying margin by controlling the atmospheric pressure by containing the magnetic disk drive apparatus in a closed chamber adjustable in atmospheric pressure.
However, in the prior arts which take measures against the flying height change due to atmospheric pressure, various problems have not been solved yet.
For example, in the arts disclosed in Japanese Patent Publications Nos. 10-177774A and 6-150522A, pressure sensors are required. However, installation of a pressure sensor considerably raises the cost of the apparatus though its use frequency is not so high as that of a temperature sensor in consideration of the ordinary use environment. Therefore, it reduces the cost performance. The arts disclosed in Japanese Patent Publications Nos. 10-177774A and 6-150522A intend to control the flying height by changing the rotational frequency of the magnetic disk, however the rotational frequency originally specifies the recording capacity and transfer speed, and it is not preferable to change the rotational frequency based on the other reasons.
Further, the arts of Japanese Patent Publications Nos. 6-176557A and 10-222945A require a large-scaled mechanism such as a closed container for sealing the magnetic disk drive apparatus in, and the pressure adjusting means, in order to measure the flying height and perform proper magnetic recording, which are adverse to the requirement for reduction in cost and size of magnetic disk drive apparatuses.